Crystalline carbohydrate derivative

ABSTRACT

α-Lactosamine hydrochloride, substantially free of β-lactosamine hydrochloride; a method of preparing α-lactosamine hydrochloride monohydrate from an anomeric mixture of lactosamine hydrochloride, including: preparing a solution including the anomeric mixture of lactosamine hydrochloride, water and at least one water-miscible organic solvent at a temperature of 0-100° C., and cooling the solution to cause crystallisation of α-lactosamine hydrochloride monohydrate; a method of preparing anhydrous α-lactosamine hydrochloride; and use of α-lactosamine hydrochloride as a food supplement or intermediate in synthesis.

This application is a continuation application of co-pending U.S. patent application Ser. No. 13/054,314, filed Mar. 25, 2011, now allowed, which is a U.S. National Phase of PCT/EP2009/059059, filed Jul. 15, 2009, which claims priority to Great Britain Patent Application No. 0812895.1, filed Jul. 15, 2008. The entire content of all of these applications is hereby incorporated by reference in their entirety.

FIELD OF THE INVENTION

The present invention provides crystalline α-lactosamine hydrochloride monohydrate, and methods of making this compound.

BACKGROUND OF THE INVENTION

Oligosaccharides have several structural forms due to their polyhydroxy character and their terminal carbonyl functions. Both aldoses and ketoses can be present in pyranose, furanose and open chain forms. Furthermore, hemiacetals/hemiketals of oligosaccharides can be characterized by both α and β anomeric linkages. The above described structural diversity makes the isolation of mono and oligosaccharides as a single chemical entity difficult. Selective crystallization of anomeric mixtures of carbohydrates can be rather difficult and quite frequently both anomers are present in crystal structures. Such difficulties often prevent the purification of important carbohydrates via crystallization. The present invention provides a facile approach for the purification of lactosamine hydrochloride via anomer selective crystallization.

Lactosamine hydrochloride is an essential disaccharide present in many natural oligosaccharide structures. To the best knowledge of the present inventors, the single anomeric form of α-lactosamine hydrochloride has never previously been synthesized and characterized. To date, only the anomeric mixture of lactosamine hydrochloride has been prepared, either via chromatography or precipitation.¹⁻⁶ The characterization of lactosamine hydrochloride has been rather modest in these publications due to the nature of the anomeric mixture of products. Such lactosamine hydrochloride products have always been described as inseparable anomeric mixtures containing both α and β nomers.

The very first methodology providing anomeric mixtures of lactosamine hydrochloride via crystallization has been described recently.⁷ The resulting product has been characterized by 1H and 13C NMR. The anomeric mixture nature of the product was indicated by the following characteristic chemical shifts: ¹H NMR (D₂O) δ=5.23 (d, 1H, H-1α., J_(1,2)=3.1 Hz); δ=4.75 (d, 0.4H, H-1β, J_(1,2)=8.43 Hz); ¹³C NMR (D₂O) δ=103.13 (C-1′ β), 103.08 (C-1′ α), 92.67 (C-1 α), 88.99 (C-1 β).

An Austrian patent application also describes the precipitation/crystallization approach, also providing an anomeric mixture of lactosamine hydrochloride.⁸ The described process gave lactosamine hydrochloride as an inseparable mixture containing 60% α- and 40% β-lactosamine hydrochloride proven by the chemical shifts of the two different chemical entities ¹H NMR (D₂O) (δ=5.28 (d, 0.6H, H-1α, J_(1,2)=3.6 Hz); δ=4.81 (d, 0.4H, H-1β, J_(1,2)=8.6 Hz).

The present invention provides crystalline a-lactosamine hydrochloride monohydrate as a single chemical entity, as demonstrated by X-ray crystallography and ¹H NMR spectroscopy. Furthermore, the present invention provides anomer selective crystallization methods for lactosamine hydrochloride producing exclusively a-lactosamine hydrochloride monohydrate. No p-lactosamine hydrochloride could be detected in the crystalline product using the most powerful analytical methodologies. The present invention has a great commercial value in large scale production of lactosamine hydrochloride providing high purity of product, which cannot be achieved by any other known purification methods.

Accordingly, the first aspect of the present invention provides α-lactosamine hydrochloride, as shown in Formula 2, substantially free of β-lactosamine hydrochloride.

This product has never previously, to the best knowledge of the present inventors, been prepared and characterized. Preferably, the α-lactosamine hydrochloride comprises less than 5 wt % of β-lactosamine hydrochloride, such as less than 2 wt %, preferably less than 1 wt %, such as 0.5 wt %, and most preferably less than 0.1 wt %.

The present inventors have selectively crystallised the α-form from an anomeric mixture of lactosamine hydrochloride, and have confirmed the identity of the crystalline product to be a-lactosamine hydrochloride monohydrate by means of X-ray crystallography. In addition, the present inventors have prepared anhydrous α-lactosamine hydrochloride.

Anhydrous α-lactosamine hydrochloride having a water content within 0-1% by weight can be made from α-lactosamine hydrochloride monohydrate by removing water of crystallisation via several methods known in the art, such as heating α-lactosamine hydrochloride monohydrate, preferably in vacuum and/o in the presence of a dessicant.

The second aspect of the present invention provides a method of preparation of α-lactosamine hydrochloride monohydrate from an anomeric mixture of lactosamine hydrochloride, comprising:

preparing a solution comprising the anomeric mixture of lactosamine hydrochloride, water and at least one water-miscible organic solvent at a temperature of 0-100° C.;

cooling the solution to cause crystallisation of α-lactosamine hydrochloride monohydrate.

Suitably, the solution is prepared by dissolving the anomeric mixture of lactosamine hydrochloride in water at a temperature of 40-100° C., and subsequently adding the at least one water miscible organic solvent.

Suitably, the method may further comprise the preliminary steps of: dissolving the anomeric mixture of lactosamine hydrochloride in water; and adding the solution to a much larger volume of acetone, such as a tenfold volume of acetone compared with the volume of the aqueous solution, to cause precipitation of a white powder, which powder is then used as the anomeric mixture in preparing the solution comprising the anomeric mixture, water and at least one water miscible organic solvent. This preliminary step forms an acetone adduct of the anomeric mixture that is insoluble in this water/acetone mixture, and so precipitates as a white powder leaving other impurities in solution.

Suitably, the at least one water miscible organic solvent is selected from the group consisting of acetone, tetrahydrofuran, acetonitrile, dioxane, aliphatic alcohols, and 1,2-dimethoxyethane. Suitably, where acetone is used as the at least one water-miscible solvent, the volume of acetone in the solvent mixture is much less than that used to create the acetone adduct, such as up to around 2-3 times the volume of the water in the solvent mixture.

Suitably, the at least one water-miscible solvent is used in greater volume than the volume of water used. Suitably, the water miscible solvent is present at at least twice the volume of water used, such as at least 2.5 or 3 times the amount of water used.

Preferably, the at least one water miscible organic solvent is at least one aliphatic alcohol ROH, wherein R is selected from methyl, ethyl, isopropyl, isobutyl and n-butyl. Preferably, the at least one aliphatic alcohol is isopropyl alcohol or isobutyl alcohol. Most preferably, isopropyl alcohol is used.

Preferably, the solution is cooled to between −5 and 30° C. in order to cause crystallisation. Preferably, the solution may be stirred during cooling in order to prevent the formation of large crystals that can capture impurities. This is particularly preferred when crystallising α-lactosamine hydrochloride on a large scale, as the formation of very large crystals in the absence of stirring can cause handling problems and damage to parts of the crystallisation vessel when the crystals are recovered from the vessel. Methods of inducing crystallisation known to the skilled man may also be employed, such as scratching the side of the crystallisation vessel with a glass rod, or providing a seed crystal in the crystallisation vessel. It is particularly preferred to use a seed crystal to induce crystallisation, as this provides better crystal purity and more rapid crystallisation, and the seed crystal used is preferably a crystal of α-lactosamine hydrochloride monohydrate made according to the method of the invention.

The purity of the starting anomeric mixture of lactosamine hydrochloride can vary from 5%-100% of the α-anomer.

The third aspect of the present invention provides a method of preparation of α-lactosamine hydrochloride monohydrate from lactosamine, comprising:

dissolving lactosamine in an aqueous hydrochloric acid solution at 40-100° C.; and

cooling the solution to cause crystallization of the α-lactosamine hydrochloride monohydrate.

Suitably, the concentration of aqueous HCl solution may vary from 0.1% to 38%.

Preferably, the aqueous HCl solution comprises at least one water miscible organic solvent. Suitably, organic solvents such as acetone, tetrahydrofuran, acetonitrile, dioxane, methanol, ethanol, propanol, butanol, or 1,2-dimethoxyethane may be comprised in the aqueous HCl solution. Preferably, the at least one water miscible organic solvent is at least one aliphatic alcohol ROH, wherein R is selected from methyl, ethyl, isopropyl, isobutyl and n-butyl. More preferably, the at least one aliphatic alcohol is isopropyl alcohol or isobutyl alcohol. Most preferably, the at least one aliphatic alcohol is isopropyl alcohol.

Suitably, the solution is cooled to between −5 and 30° C. in order to cause crystallisation. Preferably, the solution may be stirred during cooling in order to prevent the formation of large crystals that can capture impurities. As mentioned above, this is particularly preferred when performing the crystallisation on a large scale. Methods of inducing crystallisation known to the skilled man may also be employed, such as scratching the side of the crystallisation vessel with a glass rod, or providing a seed crystal in the crystallisation vessel. It is particularly preferred to provide a seed crystal to induce crystallisation, as this provides better crystal purity and more rapid crystallisation, and the seed crystal used is preferably a crystal of α-lactosamine hydrochloride monohydrate made according to the method of the invention.

The fourth aspect of the present invention provides a method of preparing anhydrous α-lactosamine hydrochloride having a water content of from 0 to 1% by weight, comprising heating α-lactosamine hydrochloride monohydrate to cause thermal removal of substantially all of the water of crystallisation.

Suitably, the heating temperature can vary from 20-172° C.

Preferably, the method comprises heating the monohydrate under vacuum. Suitably, the method may comprise the use of a dessicant to assist with removal of water of crystallisation.

The present invention further comprises the use of α-lactosamine hydrochloride which is substantially free of β-lactosamine hydrochloride in a food product or beverage, or as a functional food supplement.

The present invention further comprises the use of α-lactosamine hydrochloride which is substantially free of β-lactosamine hydrochloride as an intermediate/precursor for organic synthesis, in particular in the synthesis of human milk oligosaccharides.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows the X-ray structure of α-lactosamine hydrochloride monohydrate.

FIG. 2 shows the data obtained from X-ray diffraction studies of α-lactosamine hydrochloride monohydrate.

FIG. 3 shows the ¹H NMR spectrum of α-lactosamine hydrochloride monohydrate in D₂O immediately on preparation of the sample (3A), and a day later (3B).

DETAILED DESCRIPTION OF THE INVENTION General Procedure

A crude anomeric mixture of lactosamine hydrochloride can be prepared by using literature methods.¹⁻⁷ Different methods of preparation provide different purities of the crude mixture. However, all the expected impurities and side products present in the reaction mixtures obtained by the different methods are found to dissolve in aqueous alcohols at 40-100° C. temperatures. Stirring a solution of the crude mixture in a solvent or mixture of solvents as set out above at between −5 and 30° C. initiates the crystallization of α-lactosamine hydrochloride. Filtration, washing of the crystals with EtOH or iso-propanol, followed by a drying process at room temperature or higher temperatures provides high purity α-lactosamine hydrochloride monohydrate with a melting point of 174° C.

Alternatively, the crude lactosamine hydrochloride can be dissolved in water at 40-100° C. and subsequently the at least one water miscible solvent is added. Crystallization of α-lactosamine hydrochloride starts upon cooling and stirring.

EXAMPLES Procedure 1:

1.5 kg Crude anomeric mixture of lactosamine hydrochloride obtained according to literature procedures⁷ was dissolved in warm water (1.5 L, 50° C.). Ethanol (4 L) was added to the mixture over a period of 30 min. Then the mixture was cooled down to 0° C. and stirred for 8 h. The white crystals were collected by filtration and washed with ethanol (200 mL). Yield: 1.3 kg pure alpha anomer.

Procedure 2:

100 g crude anomeric mixture of lactosamine hydrochloride obtained according to literature procedures⁷ was dissolved in warm water (100 mL, 50° C.). i-Propanol (250 mL) was added to the mixture over a period of 10 min. Then the mixture was cooled down to 0° C. and stirred for 8 h. The white crystals were collected by filtration and washed with i-propanol (20 mL). Yield: 85 g pure alpha anomer.

Procedure 3:

100 g crude anomeric mixture of lactosamine hydrochloride obtained according to literature procedures⁷ was dissolved in warm water (100 mL, 50° C.). The solution was added to acetone (1L) obtaining a white precipitate. This powder was redissolved in water (90 mL) and i-propanol (220 mL) added to the mixture over a period of 10 min. Then the mixture was cooled down to 0° C. and stirred for 8 h. The white crystals were collected by filtration and washed with i-propanol (20 mL). Yield: 82 g pure alpha anomer.

Procedure 4:

100 g crude anomeric mixture of lactosamine hydrochloride obtained according to literature procedures⁷ was dissolved in warm water (100 mL, 50° C.). The solution added to acetone (1 L) obtaining a white precipitate. This powder was redissolved in water (90 mL) and ethanol (300 mL) added to the mixture over a period of 10 min. Then the mixture was cooled down to 0° C. and stirred for 8 h. The white crystals were collected by filtration and washed with ethanol (20 mL). Yield: 78 g pure alpha anomer.

Procedure 5:

100 g crude anomeric mixture of lactosamine hydrochloride obtained The solution was added to acetone (1 L) obtaining a white precipitate. This powder was redissolved in water (90 mL) and a mixture of ethanol and i-propanol (8% i-propanol, 220 mL) was added to the mixture over a period of 10 min. Then the mixture was cooled down to 0° C. and stirred for 8 h. The white crystals were collected by filtration and washed with the solvent mixture (20 mL). Yield: 80 g pure alpha anomer.

Procedure 6:

100 g crude anomeric mixture of lactosamine hydrochloride obtained according to literature procedures⁷ was dissolved in warm water (100 mL, 50° C.). A mixture of ethanol and i-propanol (8% i-propanol, 250 mL) was added to the mixture over a period of 10 min. Then the mixture was cooled down to 0° C. and stirred for 8 h. The white crystals were collected by filtration and washed with the solvent mixture (20 mL). Yield: 88 g pure alpha anomer.

Procedure 7:

100 g alpha lactosamine hydrochloride obtained according to procedures above was dehydrated under high-vacuum (1-10 mbar) at the temperature of 55° C. resulting in 95 g dehydrated pure alpha anomer.

Procedure 8:

100 g alpha lactosamine hydrochloride obtained according to procedures above was dehydrated under high-vacuum (1-10 mbar) at the temperature of 75° C. resulting in 95 g dehydrated pure alpha anomer.

Procedure 9:

100 g alpha lactosamine hydrochloride obtained according to procedures above was dehydrated under high-vacuum (10-15 mbar) at the temperature of 40° C. resulting in 95 g dehydrated pure alpha anomer.

Procedure 10:

100 g alpha lactosamine hydrochloride obtained according to procedures above was dehydrated under high-vacuum (10-15 mbar) at the temperature of 75° C. resulting in 95 g dehydrated pure alpha anomer.

Procedure 11:

100 g alpha lactosamine hydrochloride obtained according to procedures above was dehydrated under high-vacuum (20-50 mbar) at the temperature of 95° C. resulting in 94 g dehydrated pure alpha anomer.

Procedure 12:

100 g alpha lactosamine hydrochloride obtained according to procedures above was dehydrated under high-vacuum (50-100 mbar) at the temperature of 120° C. resulting in 94 g dehydrated pure alpha anomer.

X-Ray Crystallography

Lactosamine hydrochloride sample was made according the present invention for single crystal X-ray diffraction studies. No crystal structure of lactosamine hydrochloride was published before. However, X-ray structure of the N-acetyllactosamine is known.

Applied Investigation

i. Single crystal growing

ii. Single crystal X-ray diffraction data collection

iii. Solution of the structure

iv. Analysis of the structure and hydrogen bond network.

v. Calculation of powder diffraction data

vi. Powder data collection

Single crystals suitable for X-ray diffraction measurement could be grown by layering methanol onto water solution of lactosamine hydrochloride. This is carried out by preparing a saturated aqueous solution of lactosamine hydrochloride, filtering the solution to remove any remaining solid lactosamine hydrochloride, and then adding a small volume of water followed by careful addition of methanol.

A rather small colorless prism crystal was chosen for the measurement and fixed on the loop using perfluorinated paraffin oil. Structural data were reliable and the results are acceptable for scientific publication and/or patenting.

X-Ray Structure Determination

Colorless prism crystal (0.08×0.05×0.02 mm) of C₁₂H₂₆N₁Cl₁O₁₁, M=395,79, monoclinic crystal system, a=4.7931(8) Å, b=13.5508(19) Å, c=13.2816(19) Å, β=93.97(1) °, V=860.6(2) Å³, Z=2, space group: P2_(1, Pcalc)=1.527 g cm⁻³. Data were collected at 110(1) K, Bruker-GADDS multiwire proportional diffractometer, Cu Kα radiation λ=1.54184 Å, θ_(max)=63.3°, 6882 measured, 2059 independent reflections of which 1793 reflections were unique with I>2σ(I). Raw data was evaluated using the FRAMBO software, the structure was solved using the SIR-92 software and refined on F² using SHELX-97 program, publication material was prepared with the WINGX-97 suite, R(F)=0.061 and wR(F²)=0.156 for 2509 reflections, 254 parameters, 10 restraints. Residual electron density: 0.33/−0.33 e/Å³. Hydrogen atoms at carbon atoms were placed into geometric position while other hydrogen atoms could be found at the difference electron density map. Distance of these hydrogen atoms to the respective oxygen or nitrogen was constrained. Coordinates of hydrogen atoms were allowed to refine within a short range to the donor atom. Position of the hydrogens on the amino group was found using the riding model and their distance to the nitrogen atom was fixed. Because of the extensive hydrogen bond network, alternative positions for some of these hydrogen atoms are possible, Full data and the structure determined therefrom are shown in FIGS. 1 and 2.

1H-NMR Structure Determination

10 mg pure α-lactosamine hydrochloride was dissolved in 700 μL D₂O, then 1H-NMR spectrum was recorded immediately. A second 1H-NMR spectra was recorded a day later, by which time the clean substance had already anomerized. On first spectrum (FIG. 3, above) at 5.26 ppm the H-1 and at 4.29 ppm the H-1′ can be seen. On the second spectrum (FIG. 3, below) next to the alpha anomer already the beta appears. At 4.78 ppm H-1-beta and at 2.85 ppm H-2-beta can be seen. This experiment shows that the starting material is a clean anomer, which anomerizes at room temperature within one day.

REFERENCES

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1. A method of preparing α-lactosamine hydrochloride monohydrate from an anomeric mixture of lactosamine hydrochloride, comprising: preparing a solution comprising the anomeric mixture of lactosamine hydrochloride, water and at least one water-miscible organic solvent at a temperature of 0-100° C.; cooling the solution to cause crystallisation of α-lactosamine hydrochloride monohydrate.
 2. A method of preparing a-lactosamine hydrochloride monohydrate according to claim 1, wherein the solution is prepared by dissolving the anomeric mixture of lactosamine hydrochloride in water at a temperature of 40-100° C., and subsequent addition of the at least one water miscible organic solvent.
 3. A method according to claim 1, further comprising the preliminary steps of: dissolving the anomeric mixture of lactosamine hydrochloride in water; and adding the solution to acetone to cause precipitation of a white powder; wherein the white powder is used as the anomeric mixture in the preparation of the solution of claim
 1. 4. A method of preparing of a-lactosamine hydrochloride monohydrate from lactosamine, comprising: preparing a solution of lactosamine in aqueous HCl at 40-100° C., which solution further comprises at least one water miscible organic solvent which is an aliphatic alcohol; cooling the solution to cause crystallization of α-lactosamine hydrochloride monohydrate.
 5. A method according to claim 1, wherein the at least one water miscible organic solvent is selected from the group consisting of acetone, tetrahydrofuran, acetonitrile, dioxane, aliphatic alcohols, and 1,2-dimethoxyethane.
 6. A method according to claim 5, wherein the at least one water miscible organic solvent is at least one aliphatic alcohol ROH, wherein R is selected from methyl, ethyl, isopropyl, isobutyl and n-butyl.
 7. A method according to claim 6, wherein R is isopropyl.
 8. A method according to claim 1, wherein the solution is cooled to between −5 and 30° C. in order to cause crystallisation.
 9. A method according to claim 1, wherein the solution is stirred during cooling.
 10. A method according to claim 1, wherein a seed crystal of α-lactosamine hydrochloride monohydrate is provided during cooling to assist in inducing crystallization.
 11. A method of preparing a lactosamine-containing oligosaccharide, comprising a) preparing α-lactosamine hydrochloride substantially free of β-lactosamine hydrochloride, and b) conversion of the α-lactosamine hydrochloride into a lactosamine-containing oligosaccharide.
 12. A method of preparing a human milk oligosaccharide, comprising a) preparing α-lactosamine hydrochloride substantially free of β-lactosamine hydrochloride, and b) conversion of the α-lactosamine hydrochloride into a human milk oligosaccharide.
 13. A method according to claim 4, wherein the alcohol is ROH, wherein R is selected from methyl, ethyl, isopropyl, isobutyl and n-butyl.
 14. A method according to claim 13, wherein R is isopropyl.
 15. A method according to claim 4, wherein the solution is cooled to between −5 and 30° C. in order to cause crystallisation.
 16. A method according to claim 4, wherein the solution is stirred during cooling.
 17. A method according to claim 4, wherein a seed crystal of α-lactosamine hydrochloride monohydrate is provided during cooling to assist in inducing crystallization. 